The property of changing color when one substance is irradiated with light and then returning to its original color when such irradiation is stopped is referred to as a photochromic or phototropic property. For example, this is used in light regulating glass, etc. which contains a photochromic substance.
In addition, in the field of cosmetics also, color variable make-up, which changes color using photochromic properties, is known (Japanese Laid-open Publication No. 56-49312 and No. 56-10079), and applications in an even broader range of fields are expected in the future.
However, conventional photochromic substances have been used only for the purpose of controlling the transmission of light or for the change in color tone itself. These have not been used for controlling changes in color rendering by reflected light.
Nothwithstanding, in the case of, for example, applying foundation to the face, even if the color of the made up skin is suitable when viewed indoors, the skin appears somewhat white when viewed under the rays of the sun. On the other hand, in the case of the color of made up skin is suitable under the rays of the sun, the skin appears somewhat dark when viewed indoors. In this manner, it has become clear that even in the case of using the same foundation product, depending on the intensity of the light, the resulting image subjectively changes considerably.
Further, in regard to the relationship between light intensity and color rendering properties, the inventors conducted the following experiment to further clarify this problem.
To begin with, foundation that is used normally, and foundation products having color values that are 0.2 and 0.5 lower in appearance were applied to the faces of female panelers having average skin color. The results were judged by 10 evaluators under both indoor and outdoor conditions. Evaluations were made using the 5 grades indicated below after which the average values of the 20 panel members were determined.
______________________________________ Score Color of Made Up Face ______________________________________ +2 Dark and unnatural +1 Somewhat dark 0 Natural -1 Somewhat light -2 Light and unnatural ______________________________________
The results of this experiment are indicated in Table 1.
TABLE 1 ______________________________________ Type of Foundation Normal Color Value Color Value Product -0.2 -0.5 ______________________________________ Indoors: 200 Lux 0 +1.2 +1.3 400 Lux -1.1 0 +1.1 Outdoors: 10,000 Lux -1.3 -1.2 0 or greater ______________________________________
As is clear from Table 1 above, foundation products having a lower color value appear more natural under outdoors rather than indoors. In addition, in bright locations, even when indoors, darker colored foundations appear more natural.
In this way, unless the color value is changed according to the intensity of the light, it is not possible to maintain natural color rendering with respect to what is subjectively considered to be natural.
However, most of the conventional variable color make-up cosmetics which contain photochromic compounds use spiropyrane-based compounds. And the enjoyment of the change in color could be obtained by the cosmetics, but these could not regulate the changes in color rendering of the cosmetics with respect to light intensity. As such, the problem of conventional cosmetics with which make up skin appears attractive indoors but appears excessively white under the rays of the sun still remains unsolved.
In addition, in the case of organic photochromic agents, the degree of color change does not shift gradually corresponding to the change of light intensity, but rather, color change occurs rapidly at a certain fixed light intensity. This makes such organic photochromic agents unsuitable for regulating changes in color rendering accompanying changes in light intensity. Furthermore, in the case of use in cosmetics, etc., the safety of organic photochromic agents with respect to the human body is not sufficiently confirmed and moreover, various other issues remain unknown, such as the occurrence of photodegradation.
On the contrary, inorganic photochromic agents such as titanium oxide are thought to be unable to obtain a sufficient degree of coloring to be able to regulate color rendering at a fixed level even when blended into ingredients such as foundation due to the color change of the inorganic photochromic agent itself being comparatively small.